Fairchild AT-21 Gunner

The AT-21 Gunner was designed to fill the need for a way to train bomber aircrews, especially in regards to the operation of a bomber's machine gun defenses. In this way trainees could learn how to use a power turret or a gun on a flex mount, as well as learn to function as a member of a crew. 175 AT-21s were produced (some were manufactured by Bellanca, and some by McDonnell, but most were made by Fairchild), and they remained in service until 1944, when they were replaced by training examples of the actual aircraft in which the gunners would eventually serve.

Additional information on this aircraft
can be found at Wikipedia here.(updated February 2009)